Adenosine accumulation in Saccharomyces cerevisiae cultured in medium containing low levels of adenine

Abstract

By monitoring the in vivo incorporation of low concentrations of radiolabeled adenine into acid-soluble compounds, we observed the unusual accumulation of two nucleosides in Saccharomyces cerevisiae that were previously considered products of nucleotide degradation. Under the culture conditions used in the present study, radiolabeled adenosine was the major acid-soluble intracellular derivative, and radiolabeled inosine was initially detected as the second most prevalent derivative in a mutant lacking adenine aminohydrolase. The use of yeast mutants defective in the conversion of adenine to hypoxanthine or to AMP renders very unlikely the possibility that the presence of adenosine and inosine is attributable to nucleotide degradation. These data can be explained by postulating the existence of two enzyme activities not previously reported in S. cerevisiae. The first of these activities transfers ribose to the purine ring and may be attributable to purine nucleoside phosphorylase (EC 2.4.2.1) or adenosine phosphorylase (EC 2.4.2.-). The second enzyme converts adenosine to inosine and in all likelihood is adenosine aminohydrolase (EC 3.5.4.4).

Adenine deaminase and adenine utilization in Saccharomyces cerevisiae

“…Marmocchi et al (18) have reported the partial purification of ADA from commercial baker's yeast. The demonstration of ADA in S. cerevisiae confirms previous hypotheses of its existence, based upon the kinetics of inosine formation from exogenous adenine in vivo (5,13) and the report of very low levels of ADA activity in crude cell extracts (38). The involvement of ADA in balancing adenine and guanine derivatives in vivo has been suggested (5); however, direct study of this pathway has been complicated by the inability of wild-type yeast to incorporate exogenous adenosine (1) and the requirement of either APRT or AAH for growth of purine auxotrophs (36).…”

“…Commercial baker's yeast exhibits the capacity to convert adenine into adenosine (13) and to deaminate adenosine into inosine (18); however, this pathway was inefficient compared with the AAH and APRT pathways, presumably owing to the poor conversion rate of adenine into adenosine (9, 13). Marmocchi et al (18) have reported the partial purification of ADA from commercial baker's yeast.…”

“…Adenine enters yeast metabolism (5, 36) via two pathways: deamination by adenine aminohydrolase (AAH) into hypoxanthine, followed by conversion into IMP, and conversion by adenine phosphoribosyltransferase (APRT) into AMP, followed by deamination into IMP. Laten et al (13) …”

“…Adenine enters yeast metabolism (5,36) via two pathways: deamination by adenine aminohydrolase (AAH) into hypoxanthine, followed by conversion into IMP, and conversion by adenine phosphoribosyltransferase (APRT) into AMP, followed by deamination into IMP. Laten et al (13) ADA. The amount of adenine incorporated via this pathway is extremely low (less than 1% of that of either AAH or APRT), consistent with the reported irreversibility of NH and the poor reactivity of adenosine with the reversible activity of purine nucleoside phosphorylase (9).…”

Role of adenine deaminase in purine salvage and nitrogen metabolism and characterization of the ade gene in Bacillus subtilis

“…This finding indicates that conversion of adenine to adenosine catalyzed by adenosine phosphorylase followed by phosphorylation of adenosine is not an alternative pathway under the conditions described. In S. cerevisiae, adenine can be converted to adenosine, which can accumulate in the cytoplasm (26). Such an accumulation could not be demonstrated for B. subtilis (data not given).…”